– remove the bearings from the EFE front wheel, and take the tube which is in between them. Do the same with the GSX-R one.
– you will find out the EFE one is 16mm longer than the GSX-R one. It needs shortening 16mm.
– buy some bearings which fit in the GSX-R wheel and on the EFE spindle. I don’t remember exactly the sizes, but you need bearings with the ID of the EFE ones, and the OD and width of the GSX-R ones. They were off the shelf in the local bearings shop.
– the tubes in the bottoms of the EFE forks are now too short. Make some new ones which are 8mm (each) longer.
– the EFE speedo drive will fit after a little bit of material has been removed. Offer it up on the GSX-R wheel and you’ll see exactly where.

And now, with that nice 3-spoke wheel, it would be a shame not to upgrade the brakes as well.
The Slingshot Nissin 4-pots, and the later GSX-R models’ Tokico 4- and 6-pots all fit on the EFE forks, 90mm spacing between the bolts. But the Slingshot discs are too large.
Now Suzuki had thought about this and launched the GSX600F in the late eighties, this bike has brake discs that fit perfectly on the GSX-R wheel and are small enough to accept the more modern calipers when mounted in the EFE forks. All it needs is some small rings to space out the calipers a bit towards eachother.
Use the EFE caliper mounting bolts, they are longer than the GSX-R ones.